Heat stress constitutes an advantageous system to study inducible gene expression, and provides probably the best system to study how mRNA translation is regulated. This project will characterize translational regulation at different stages of chronic mild heat stress such as occurs during fever, and identify the molecular mechanisms responsible for heat- induced regulation. Alterations in ribosome activity and mRNA translational efficiency will be precisely quantified by polysome analysis and Norther blot analysis. Protein synthetic patterns also will be determined. Factors causing global protein synthesis repression, global protein synthesis restoration due to adaptation, and preferential translation of heat stress mRNA will be characterized, and the active factor purified. Purification will be primarily accomplished by cell free translation activity analysis. Selection of the appropriate assay samples will be based on the kinetics of global repression and restoration, and on the kinetics of preferential translation of heat stress protein (HSP) mRNAs. The possibility that HSPs influence preferential translation of thermotolerance will be investigated. Heat-induced phosphorylation changes will be correlated with translation status. Candidate switch molecules will be further characterized with reference to purification results as achieved above. HSP 28 phosphorylation will be analyzed in detail. It is a major phosphorylated protein in cells perturbed by heat, growth factor, arsenite, etc. The HSP 28 kinase will be purified. Molecular pathways leading to HSP 28 phosphorylation will be characterized, and the effects of phosphorylation on HSP 28 function evaluated.